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A guide to carbon profiling

26 March, 2009

Sustainability editor Hattie Hartman investigates a clever way of quantifying a building’s total carbon use

‘We did not set out to be green. This is just a common-sense way of finding the best design solution,’ says Romi Dahele, international director of Sturgis Associates. He’s talking about ‘carbon profiling’, a technique employed during his practice’s recent refurbishment of a mixed-use building in Bloomsbury, London. Carbon profiling is the calculation of the total (embodied and operational) energy footprint, estimated over a building’s whole life.

Before the £32 million refurbishment, undertaken for City Offices, 111 New Cavendish Street was an average 1960s-built, mixed-use building. The new scheme retains the original concrete frame and foundations, but cladding, services and internal finishes were stripped out. The residential units remained occupied throughout. To increase the floor area – and value – recesses and setbacks were infilled.

Part L of the Building Regulations requires the modelling of a building’s predicted operational carbon, but Sturgis also modelled embodied carbon, and was able to convey the results in simple, client-friendly language.

The embodied energy and estimated design-life of each component of the building – foundations, structure, floors, external and internal walls, internal finishes, roof and services – is quantified with bespoke in-house software. The resulting calculations are used to inform decisions, such as the choice of cladding. For operational carbon, all the usual daylight and solar-gain modelling processes were used to determine shading requirements.

For Sturgis, carbon profiling evolved organically, rather than as a deliberate strategy. The practice grew weary of seeing perfectly good parts of buildings ‘trashed’. ‘During the boom, it was easier to knock stuff down, but as an architect you recognise the parts of a building that have quality. Eventually we realised we had pioneered a new approach and so we decided we should give it a name – carbon profiling,’ says Dahele.

‘A number of our clients, including British Land, Tishman Speyer and LaSalle, are looking to incorporate this into their thinking for the future,’ adds managing director Simon Sturgis.

The practice recently presented carbon profiling at a UK Trade and Investment seminar in India, where, according to Dahele, there is no interest in sustainability unless it makes money. Sturgis has recently opened an office in New Delhi with an eye on this emerging market.

Whether in London or New Delhi, carbon profiling is an intelligent approach to giving buildings a second, or even third, life.

What is carbon profiling?

Sturgis carries out carbon profiling using a bespoke software program that measures the embodied carbon of a building over its lifetime to ascertain its whole-life carbon footprint. Part L requires a calculation of operational energy-use, the Building Emission Rate (BER), which is calculated in kgCO2/m2/year. Carbon profiling uses these same units to measure Embodied Carbon Efficiency (ECE), including allowances for the demolition and transport associated with the building. The total annual carbon cost of a building is the sum of the BER (operational energy) and the ECE (embodied energy).

Each component of a building is analysed. For example, an aluminium panel and glass cladding system can be compared with a concrete panel and glass cladding system. The concrete system uses about 20 per cent less carbon to construct than the aluminium and will last approximately two to three times longer. Therefore, the ‘carbon cost’ over time is significantly less for concrete than for aluminium.

This approach enables us to design with longer life, more carbon-efficient components and quantify the value associated with the reuse of the existing structure and components. It also allows clients to make more informed choices about design options, based on quantified information.

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